Description
Williams Controls 118365 (also catalogued as WM-778-100) is a 70 PSI air pressure protection valve used on heavy-duty truck air systems to prioritize service brakes over secondary air consumers. The valve stays closed until upstream system pressure climbs above 70 PSI, then opens to feed downstream auxiliaries; it re-closes when pressure drops back below 70 PSI, ensuring the brake reservoir stays charged. Plumbed via two 1/8″ NPT ports and rated to 150 PSI maximum, -40°F to 180°F service. Meets FMVSS 121.
Specifications
| Manufacturer | Williams Controls |
|---|---|
| Part Number | 118365 |
| Model | WM-778-100 |
| Part Type | Pressure Protection Valve (PPV) |
| Nominal Opening Pressure | 70 PSI (482 kPa) |
| Maximum Operating Pressure | 150 PSI |
| Operating Temperature | -40°F to 180°F (-40°C to 82°C) |
| Ports | (2) 1/8″ NPT |
| Compliance | FMVSS 121 |
Cross References
This valve replaces or is equivalent to the following part numbers:
- Williams Controls: 118365, WIL118365, WM-778-100
- Chelsea: 378414
Applications
This pressure protection valve is used on Class 6–8 truck and trailer air systems to protect primary brake supply pressure from secondary auxiliary loads. Common applications include:
- PTO and pump air controls (Chelsea 378414 replacement on truck PTO circuits)
- Secondary air horns, air seats, and accessory air consumers
- Trailer brake supply protection
- Air-shift transfer cases and drivetrain air actuators
- Williams Controls throttle and accessory air sub-systems
Verify your existing PPV opening pressure (70 vs 85 vs 95 PSI) before ordering — the 118365 is specifically the 70 PSI variant. Mount with port orientation per OEM service literature; flow direction is bidirectional but the valve must be installed with the supply port upstream.
